The image formation process utilizing the electrostatic electrophotographic system generally involves a charging step, exposure step, transfer step, developing step, peeling step, cleaning step, charge removing step and fixing step. The process of forming an image is carried out in the following manner. First, the surface of a photoconductor driven with rotation is uniformly charged by a charger. Then, the surface of the charged photoconductor is irradiated with laser light by an exposure apparatus to form an electrostatic latent image, in succession, the electrostatic latent image on the photoconductor is developed by a developing device to form a toner image on the surface of the photoconductor. Moreover, the toner image on the photoconductor is transferred to a transfer-receiving material by a transfer device. Thereafter, the transferred toner image is fixed on the transfer-receiving material by heating using a fixing device to form an image. Also, the toner left untransferred on the photoconductor is removed by a cleaning device and recovered to a prescribed recovery section. Moreover, the surface of the photoconductor cleaned is subjected to a charge removing device to remove a residual charge and prepared for the next image formation.
Recently, the use of toners (small-particle diameter toners) having a volume average particle diameter of 7 μm or less have come to be the mainstream in order to improve the reproducibility of dots for the purpose of improving a higher quality image in an image forming device. The small-particle diameter toner has high cohesive force and high adhesion, posing the problem concerning less transfer efficiency when a toner image is transferred to a recording medium from a photoconductor drum.
As the method that solves this problem, a method of adding a large-particle diameter external additive to a toner is disclosed in, for example, the Japanese Unexamined patent publication of No. 2000-81723.